Process for joining metallic surfaces and products made thereby



J- H- OLSON July 26, 1966 PROCESS FOR JOINING METALLIC SURFACES ANDPRODUCTS MADE THEREBY Original Filed April 21, 1954 INVENTOR. J22 0/ 07ATTORNEYS United States Patent M 3 262,490 PROCESS FOR JOINIl-IGMETALLIC SURFACES AND PRODUCTS MADE THEREBY John H. Olson, Westfield,N.J., assignor to Chrysler Corporation, Highland Park, Mich., acorporation of Delaware Original application Apr. 21, 1954, Ser. No.424,680, now Patent No. 3,129,502, dated Apr. 21, 1964. Divided and thisapplication Sept. 20, 1963, Ser. No. 310,256

2 Claims. (Cl. 165-10) The present application is a division of mycopending application Serial No. 424,680, filed April 21, 1954, nowPatent 3,129,502, granted April 21, 1964.

This invention relates to methods for securely, firmly, and intimatelyjoining or uniting metallic parts of a single or plurality of members bya metal bond. It is especially concerned with an electroless plate bondof such parts; and with the heat treatment of parts so bonded. Also withthe simultaneous electroless plating and bonding of metallic parts. Ithas particular application to parts of a ferrous character. Moreover, itrelates to novel structures such as heat exchangers, and rotaryregenerators for gas turbines comprising a composite of thin sheets ofirregular or other shaped character, in the making of which thesebonding methods are employed to provide a metal bond substantiallyimpervious to the passage of gas and which also may be hard.

It is known to join metallic surfaces by soft soldering, hard soldering,(silver brazing) or copper brazing. These procedures require the use ofa flux and/ or an inert atmosphere and a metal or alloy of lead, tin,brass, copper, silver, phosphorous. Moreover, since the brazing musttake place at high temperatures (over 2000 F. in the case of copperbrazing) distortion, buckling and grain growth in the iron structure caneasily occur at such high temperatures when joining metals such as lowcarbon steels.

My invention avoids these difliculties in that neither high heat normelting of the bonding metal is essential to effect a bond. However,these steps may be employed as supplemental procedures in my inventionfor further advantages that will flow therefrom but in such cases one ormore of the difficulties of distortion and grain growth are inhibitedbecause of the basic steps which precede such heating and/or melting andbecause lower temperatures are then feasible. Moreover, in my inventionthe resulting product has an oxidation resisting plate protecting alliron surfaces.

Broadly stated, my invention comprises bringing the portions of theparts to be bonded into juxtaposition, preferably into contact with eachother, better yet pressure contact, and electroless plating these partscontiguous with these portions, while maintaining the parts in theirjuxtaposed relationship, for a sufficient time to form an adherentconnecting web of fillet of deposited alloy metal between the portionsto be bonded. The plating is carried out by immersing the portions to bebonded, while maintained as stated above, in an electroless plating bathor fluid whereby under the catalytic action of the met-a1 of which theparts are made or of some other metal applied thereto, the bonding metalis deposited out of the bath and onto the portions of the parts to bebonded. The action is one of chemical reduction. Not only are theimmersed parts plated with the metal given up by the bath, but where theaction is continued for a sufficient time, tying webs of fillets areformed contiguous with the portions to be bonded which adequately joinand hold the parts together.

By electroless plating I mean a chemical plating 3,262,490 Patented July26, 1966 process, examples of which are hereinafter given wherein analloy metal comprising nickel and phosphorus is deposited from a platingbath without the use of electric current and by reason of a catalyticmetal present in or on the structure to be plated.

Electroless plating is further advantageous in that the alloy depositsobtained have a melting point facilitating fusion of the plate bond.

In actual practice I have found that a plate of at least about 0.0003inch thickness is necessary to produce a satisfactory mechanical bond.By a satisfactory mechanical bond I mean one which will permit ordinaryhandling of the bonded structure and its subjection to reasonablevibration and/or shock without failure of the bond or stated otherwise,I mean a bond which permits use of the bonded part for its intendedpurposes. For example, where the bonded parts are to be used for heatexchangers, the bond should provide a seal for the passage of air andcombustion gases and be good enough to prevent the gases from diffusingthrough the joint. It will be understood that the thickness will beinfluenced somewhat by how well the parts are held together duringplating, that is to say, whether or not there is pressure contactbetween the parts.

Heat treatment of the bonded part at a temperature below the meltingpoint of the plate will improve the strength and hardness of the jointand may in certain cases permit the use of plates of lesser thicknessthan that above. In fact, a plate of even about 0.0002 inch thicknesswill give a satisfactory mechanical bond if the surfaces joined by theplate are thereafter heated to the fusion temperature of the bondingmetal plate, this being preferably carried out in a non-oxidizingatmosphere. This will also render the bond substantially non-porous. Itmay also be noted that although the plate will flow, the parts will notshift during holding since there is a substantially parentmetal-to-metal contact. This is of importance where a large number ofparts must be bonded together within a limited space.

The combination plating and heating is also of especial significancewhere a strong metal bond is required in a structure employing readilyoxidized parts such as mild or low carbon steel and with a minimumplate. The plating operation renders the surfaces of the bondedstructure resistant to oxidation during subsequent heating and the platebond holds the parts together during heating. Moreover, by obtaining analloy plate bond, a sufiiciently low melting point may be available suchthat the structure, especially where of a low carbon steel, may beplated and heated without deleterious buckling, distortion or graingrowth on the steel during heating. Tensile readings on two sheet testspecimens indicate a joint strength in tension of 20,000 to 23,200 lbs.per sq. in.

Where the heating procedure is employed, the bond may be effected byeither first bonding the parts by plating and then heating or by firstseparately plating the parts and then heating the parts while heldtogether. The latter procedure requires good pressure cont-act betweenthe surfaces to be bonded and cannot be used, for example, where theplated parts would have to be shaped after plating as the plate depositdoes not permit of sharp bending. Moreover, where the parts areseparately plated before joining, the heating step should be carried outin an atmosphere which will not oxidize the metal, that is to say, aneutral atmosphere, for instance in an atmosphere of hydrogen or crackedgas. Where the parts are however bonded by plating, heating in a neutralatmosphere preferred is not always necessary.

The plating process I use and which is generally known in its broadaspects involves the reducing action of hya pophosphites in a solutionof nickel salts at 180 F. or higher preferably 180200 F. or above in thepresence of certain catalytic metals. The reaction may be expressedgenerally by the following equations:

NaH PO NaH2PO3 H2 The hypophosphite undergoes oxidation and the nickelis reduced. No electric current is involved in the deposition. Thenickel plating process may be carried out with acid or alkalinesolutions. The deposition of nickel may be carried out in conjunctionWith any catalytic material which will initiate at its surface the abovereaction. Iron, nickel, gold, cobalt, aluminum are especially goodcatalysts. Other metals which are non-catalytic or which are temporarilypassivated catalytic metals, such as brass, copper, and platinum, may benickel plated by special methods, such as by using particular alkaineplating solutions, omitting ammonium salts for brass and copper; makingmomentary contact of the surface of the parts with a moreelectronegative metal such as aluminum, iron or steel or by depositingminute amounts of catalytic metal such as palladium or rhodium on thenon-catalytic one by dipping the parts after cleaning, into a solutioncontaining one of these metals. Once the plating starts, the reductioncontinues on the phosphorous-nickel first deposited. Zinc gives poordeposits and lead and cadmium are not favorably affected. It has beenfound, however, that the commonly used zinc immersion pre-treatment ifapplied to aluminum or alloys such as 38 and 24S alloys(aluminum-manganese and aluminum-copper respectively) provides a goodbase for securely bonding electroless nickel-phosphorous.

Although similar plating procedures using alkaline baths may be followedwith respect to obtaining a cobalt plate, these deposits have been foundto be porous and of poor physical character not suitable for thephysical bonds required in this invention.

An object of my invention is to join or unite metallic parts of a singleor plurality of members by a metal bond produced by electroless plating.

Another object is to join or unite metallic parts as aforesaid and tosubsequently subject the plated composite structure to heat treatment toincrease the strength of the bond.

Still another object is to simultaneously electroless plate and bondmetallic parts by a metal bond.

A specific object is to bond metallic parts by first electroless platingthe same and then heating the parts to the melting point of the platewhile holding the parts in faceto-face contact to effect the bond.

A further object is to join or unite metallic parts in accordance withany of the preceding objects, and to subsequently subject the platedstructure to heat treatment at or above the fusion temperature of thebonding metal of the plate but below the fusion temperature of thebonded parts.

Still a further object is to join or unite parts composed of mild or lowcarbon steel or of which one of these is a member, by a strong solidbond or joint of metal impermeable to the passage of gas, by electrolessplating the parts to bond the same and provide a corrosion and oxidationresisting metal protective layer for the steel and then heating theparts to the melting point of the bonding metal but below that of thesteel parts.

Another object is to provide a rotatable regenerator structure for a gasturbine power plant or the like comprising a cellular core having amultiplicity of elongated cells defined by wall portions abutting eachother along seams closed to the passage of gas by a metallic bond orlayer comprising an electroless plate.

A further object is to provide a regenerator structure as in thepreceding object wherein the abutting parts are bonded by a fusedelectroless metal plate.

These and other objects of my invention will be apparent from thefollowing description and the accompanying drawings wherein I haveexemplified my invention as applied to a regenerator or heat exchangestructure such as disclosed in the copending application of GeorgeHuebner et al. Serial No. 389,094, filed October 29, 1953.

In the drawings:

FIGURE 1 is a sectional view of a rotatable regenerator unit for thepower plant of a gas turbine engine;

FIGURE 2 is a detail sectional view of a portion of the core of theregenerator of FIGURE 1;

FIGURE 3 is an enlarged sectional view of the circled portion in FIGURE2 showing the manner of bonding adjacent layers of the regenerator core;and

FlGURE 4 is a detail sectional view of a composite core made up ofsubstantially flat elements.

As seen in FIGURES l and 2, the regenerator core 10 smooth sheet metalstock which may be of a mild or low may consist, for example, of aplurality of layers 12 of smooth sheet metal stock which may be of amild or low carbon steel composition and a plurality of layers 14 ofcorrugated metal sheets which also may be of a mild or low carbon steelcomposition, which layers 14 alternate with the layers 12. These layers12 and 14 are arranged concentric to or in a spiral about a hub 16 andsurrounded by a confining rim member 18. The layers 12 and 14 in thecore structure 10 may be constituted of concentric rings, or the coremay be made up by a spiral winding of a pair of continuous sheetsforming the layer 12 and 14.

As seen in FIGURE 2, the alternate arrangement of corrugated and flatlayers 14 and 12 respectively form passages or recesses 20 extendingaxially of the core adjacent the joints 28, 30 formed at the contactingportions there shown these layers. Each of these passages 20 is definedby spaced wall portions 22 and 24, respectively, of the layers 12 and14, respectively, and by spaced corrugations 26 of the layer 14. Thecorrugations 26, as shown, have ofiset peak portions at the joints 28,30 in contact with adjacent layers 12 of the core, these peak portionsdefining apices of the passages or recesses 20 with the layers 12. Whenthis core is treated in accordance with the present invention, each ofthe contacting peaks of the corrugations 26 will be bonded to theadjacent layer 12, as seen in FIGURE 3, by webs or fillets 32 of metalin said apices of the passages 20 which securely hold these layerstogether and provide a gas-impervious joint between the adjacentpassages 20.

The following examples will serve to illustrate the manner of carryingout my invention:

Example I A rectangular core section 1" x 2.2" x 3" of the layercharacter shown in FIGURE 4 and consisting of 93 plates was suitablyheld in a fixture to obtain pressure contact between the adjacent sheetsat the peak of the corrugations and immersed in an electroless chemicalsolution of 4.7 liters capacity for 12 /2 hours. The section was made upof alternate layers of corrugated and flat sheets of low carbon steel of0.002 thickness and contained 1230 sq. in. of surface area disregardingthe corrugations.

The bath was of the acid type and contained the following ingredients:

10 grams per liter of nickel chloride (NiCl -6H O);

10 grams per liter of sodium hypophosphite 8.9 grams per liter of citricacid (C H O -H O);

15 grams per liter of dibasic sodium phosphate (Na HPO The dibasicsodium phosphate in this bath serves as a buffer maintaining the pH at 4to 6. The amount of citric acid employed is sufficient to make a newacid bath having a pH of about 6. The nickel chloride and sodiumhypophosphite react upon immersing the steel structure in the bath togive a catalytic deposit of nickel-phosphorous on the steel. Thisplating bath has the ability to plate at the rate of about 0.0002 inchper hour where the area plated does not exceed about 20 sq. inches perliter of solution.

The section was maintained in the bath for twelve hours after which itwas removed and found to have a plate layer of nickel-phosphorous ofabout 0.0005 inch thick. Based on chemical tests the amount ofphosphorous in the plate was about 14.15 to 14.75 percent.

An examination of the section showed the adjacent layers to have theirfaces plated and the peaks of the corrugations bonded to the adjacentlayers by fillets of the plating metal. These fillets were continuousthroughout the length of the core and the plating was substantiallyuniform. There was a good physical bond between the plates and theassembly was free of distortions. A structure of this character issuitable for heat exchange purposes.

Example II A core section plated as in Example I was heated for twentyminutes at 1650 F. in a neutral atmosphere (cracked gas). At thistemperature the metal of the plate was molten and fiowed towards thejoints between the corrugations of the layers 14 of the section and thecontacting faces of the layers 12. There was a tendency for the platebetween the corrugations to become somewhat thinner than the originaldeposit, some of the plate at these points shifting to the jointsbetween the adjacent layers. The resulting structure showed improvedstructural strength due to the flow of plate metal to the joints toproduce fillets of increased section. The hardness of the plate wasreduced from about 480 Vickers to about 250 Vickers, this also beingbelieved to enhance joint strength and to improve ductility.

Example III A regenerator unit core, as seen in FIGURES 1 and 2,suitably held in a fixture which may be the rim 18, was immersed in anelectroless chemical plating solution of 86-gallon capacity. The unitwas 20 /2" in diameter and 3" thick. It was made up of alternate layersof corrugated and flat sheets oflow carbon steel of 0.002 thickness andcontained 725 sq. ft. of surface area disregarding the corrugations.

The bath which was of the acid type, contained the followingingredients:

grams per liter of nickel chloride (NiCl -6H O); 10 grams per liter ofsodium hypophosphite 8.9 grams per liter of citric acid (C H O -H O);37.5 grams per liter of dibasic sodium phosphate (Na HPO The dibasicsodium phosphate in this bath serves as a buffer maintaining the pH at 4to 6. The amount of citric acid employed is sufficient to make a newacid bath having a pH of about 6. The nickel chloride and sodiumhypophosp'hite react upon immersing the steel structure in the bath togive a catalytic deposit of nickelphosphorous on the steel. This platingbath has the ability to plate at the rate of about 0.0002 inch per hourwhere the area plated does not exceed about 20 sq. in. per liter ofsolution.

The regenerator unit was maintained in the bath for twelve hours afterwhich it was removed and found to have a plate layer ofnickel-phosphorous at least 0.0004 inch thick. The adjacent layers hadtheir faces completely plated and the peaks of the corrugations werestrongly bonded to the adjacent layers by fillets of the plating metalwhich fillets were continuous throughout the length of the core. Thephysical bond was good and the structure was free of distortion.

6 Example IV A composite structure of alternate flat and corrugatedsheets, five in number, 1" x 3" and having a surface area of 30 sq. in.excluding the corrugations, were held together by a wire and immersed ina nickel-phosphorous plating bath of alkaline character for four hoursand upon removal was found to have a plate thickness of 0.0008".

The solution contained the following ingredients:

30 grams per liter nickel sulphate (NiSO -6H O);

50 grams per liter of ammonium chloride (NH Cl); grams per liter ofsodium citrate (Na C5H5O7 10 grams per liter of sodium hypophosphite(NQHzPOg'HzO) To the above was added enough ammonium hydroxide (NH OH)to bring the pH value of the solution to about 9.0. The bond wassatisfactory.

Example V A composite structure as in Example IV but made up of fouralternating flat and corrugated low carbon steel sheets 1" X 1" heldtogether by a wire, was plated in a solution of the same character asthat of Example IV but wherein 30 grams of nickel chloride (NiCl -6H O)was substituted for the nickel sulphate. This structure was maintainedimmersed in the solution for one hour. The plates were bonded togetherby a nickel phosphorous plating of 0.00031" thickness.

Example VI A structure as in Example V was immersed in the solution forone-half hour instead of one hour and upon removal was found to have aplate thickness of 0.00021". Although this plate bonded the layerstogether, it was insufficient to provide a satisfactory mechanical bond.However, upon heating the bonded and wired structure to 1850 F. in aninert atmosphere of dry hydrogen for a short time, the character of thebond was sufficiently improved to be mechanically satisfactory.

Example VII Example VIII Two pieces of diameter drill rod were wiredtogether to form a 1" lap joint with a third piece 1" long. This wasimmersed in a solution as in Example I for 3 /2 hours. The platingthickness was 0.0003 on the sections of rod beyond the lap joint. Afterheating for one hour at 750 F. the wire was removed and the structuretested in tension. It was found that a weight of 417 grams could besupported before the joint failed. This would appear to correspond to anappreciable tensile strength.

Example IX A heat exchange unit for the oil cooler of an automatictransmission had its heat exchange element plated by electroless nickelon its outer sides only and the halves of its split steel water housingplated by electroless nickel on all faces, by immersing in an acidsolution according to Example I. The nickel-phosphorous plate depositwas 0.001" thick. After plating, the parts were assembled and the casingparts held between clamps with their joint faces in abutment and theassembly heated to 1800 E, which is above the fusion temperature of thenickelphosphorus plate. Heating was carried on in a nonoxidizingatmosphere such as cracked gas for one-half hour during which period theparts of the casing became securely bonded by the plate. This unit and asimilar one which had been electroless plated after the housing partshad been bonded by copper brazing and not heated to the fusiontemperature of the plate, were then tested for anti-corrosive propertiesby circulating a hot corrosive solution of salt through the units for500 hours. This solution consisted of 30% alcohol, 70% water, and 522parts per million of sodium chloride.

The two units were then cut open and examined. The copper brazed unitwas found to contain numerous areas of rust whereas the plate-fused unitwas free of any rust and in excellent condition. This indicates thatheating of the nickel-phosphorus plate renders the treated structurehighly resistant to corrosion. This improvement is believed due to thefact that heating of the plate eliminates any pre-existing porosity ofmicroscopic cracks in the plate and such prevents penetration of thecorrosive material to the under ferrous layer.

In the above processing, the baths were made up by heating the nickelhypophosphite and buffer salts to 190 F. but at all times remainingbelow the boiling point of this solution. The articles to be plated werethen brought into contact with the solution as by immersing in the bathwhile preferably maintaining the bath at a temperature above 180 F. butbelow the boiling point of the solution (about 205 F.).

In operation of the bath it is desirable to replace the hypophosphite,nickel and the dibasic sodium phosphate after long periods of operation.The thickness of the ferrous sheets or structure plated is notimportant. They may be thin or thick. In the acid solutions the dibasicsodium phosphate may be replaced with the corresponding potassium orammonium salt. The ammonium salt produces the highest plating rate butthe deposit has larger crystals. Moreover, the potassium salt appears togive a somewhat faster plating rate than the sodium salt. In all cases asubstantially uniform plate is obtained. It is found that thealkaline-type bath usually boils off ammonia and therefore is not asgood as the acid bath from the practical operational standpoint.

In connection with the above examples, it has been found that the plateof Example I will contain about 14% phosphorous; that the plate ofExample III will contain about 10 to 12% phosphorous; the plate ofExample IV will contain about 2.9% phosphorous, and that the plate ofExample VII will contain about 6 /2% phosphorous. Thus the amount ofphosphorous in the nickel-phosphorous plate obtained by any inventionmay be varied between the amounts given by a proper selection of thesolution and its contents.

From the foregoing description of my invention, it will be apparent thatI have provided a novel and eflicient method for joining metal parts bya metal bond and provide a metal bond whose composition is particularlyadapted for the purposes described. The above description and examplesare intended as illustrative only. Hence any modification of orvariation therefrom or equivalent thereof which conforms to the spiritand intent of my invention and comes within the scope of the appendedclaims are contemplated.

I claim:

1. A metallic structure comprising a plurality of metallic partsarranged in a joint forming relationship whereby an elongated recess isformed between said parts having its apex in said joint, a substantiallyuniform and continuous layer of nickel phosphorous alloy having betweento 97.5% nickel and 2 /2 to 15% phosphorous produced by electrolessplating over said parts contiguous said joint and providing a continuoussubstantially uniform fillet-like web in the apex of said recess, saidlayer bonding said parts together and providing a highly corrosionresistant and gas tight joint between said parts in said joint, saidlayer having a thickness of at least about 0.0002".

2. A metallic structure comprising a plurality of thin metal layers atleast alternate ones of which are of undulated form providing adjacentelongated peaks and valleys, said layers being arranged with the valleyportions of the undulated layers in substantial contact with portions ofthe immediately adjacent layers, the said layers forming adjacentelongated passages spaced by said substantially contacting portions, andan adherent connecting fillet-like web of metal between said layersadjacent said substantially contacting portions in said passagestenaciously bonding said layers together and providing a highlycorrosion resistant and gaseous seal between said adjacent passages atsaid portions, said web consisting essentially of nickel phosphorousalloy having between 85 to 97.5% nickel and 2 /2 to 15% phosphorousproduced by electroless plating, said web having a thickness of at leastabout 0.0002".

References Cited by the Examiner UNITED STATES PATENTS 2,154,217 4/1939Savage 29-1573 2,532,283 12/1950 Brenner et al l17130 X 2,602,645 7/1952Benenati et al -10 X 2,757,628 8/1956 Johnston 113-118 2,767,111 10/1956Otto et al 148-6.15 2,787,565 4/1957 De Pretto 148-6.15 3,045,982 7/1962Kohler et a1 165l0 3,081,822 3/1963 Wolansky et al. 165--10 FOREIGNPATENTS 487,263 6/1938 Great Britain. 531,610 1/1941 Great Britain.

OTHER REFERENCES National Bureau of Standards Journal of Research, vol.39, No. 5, pp. 385-395, November 1947.

Zeitschreft Fur Anorganische Und Allgemeine Chemie (Scholder et al.),vol. 198, No. 4, pp. 329-351, 1931.

ROBERT A. OLEARY, Primary Examiner.

CHARLES SUKALO, Examiner.

A. W. DAVIS, Assfistant Examiner.

1. A METALLIC STRUCTURE COMPRISING A PLURALITY OF METALLIC PARTSARRANGED IN A JOINT FORMING RELATIONSHIP WHEREBY AN ELONGATED RECESS ISFORMED BETWEEN SAID PARTS HAVING ITS APEX IN SAID JOINT, A SUBSTANTIALLYUNIFORM AND CONTINUOUS LAYER OF NICKEL PHOSPHOROUS ALLOY HAVING BETWEEN85 TO 97.5% NICKEL AND 2 1/2 TO 15% PHOSPHOROUS PRODUCED BY ELECTROLESSPLATING OVER SAID PARTS CONTIGUOUS SAID JOINT AND PROVIDING A CONTINUOUSSUBSTANTIALLY UNIFORM FILLET-LIKE WEB IN THE APEX OF SAID RECESS, SAIDLAYER BONDING SAID PARTS TOGETHER AND PROVIDING A HIGHLY CORROSIONRESISTANT AND GAS TIGHT JOINT BETWEEN SAID PARTS IN SAID JOINT, SAIDLAYER HAVING A THICKNESS OF AT LEAST ABOUT 0.0002".